1. Field of the Invention
This invention relates to radio-frequency transformers and more particularly to such transformers adapted for use in coupling low-impedance conductive-body antennas to associated radio-frequency apparatus.
2. Description of the Prior Art
In U.S. Pat. Nos. 2,923,813; 2,971,191; 3,007,164 and 3,066,293 and in the applications referred to herein under the heading RELEVANT COPENDING APPLICATIONS this inventor described several approaches to utilizing as antennas conductive structures, such as automobile bodies. One of the major problems in coupling R. F. energy into or out of such conductive-body antennas is the extremely low impedance looking into the conductive body at the discontinuity into which or from which R. F. energy is to be introduced or extracted from the conductive body. This problem is a particularly acute one at the radio frequencies associated with the medium wave A-M radio broadcast band (approximately 550 to 1600 kiloherz).
To help solve this problem this inventor conceived, reduced to practise and has described in his prior patents and applications a voltage and impedance transformer usable at radio frequencies which comprised a one-turn conductive sheath or tube acting as a primary, the secondary being formed by a conductor passing through the inner opening of the sheath or tube 8 or 9 times (when used at medium wave frequencies) and, hence, being very tightly coupled, magnetically, to the singleturn primary of the transformer. This design reduces unwanted electrostatic signals and noise in the transformation process. To further increase the coupling between the single turn primary and its secondary and to increase the inductance of the single turn primary to a level such that it matches the inductance of the conductive-body as it appears at the discontinuity in the conductive body a series of ferrite, high-permeability beads is applied so that it covers completely the one-turn primary sheath or tubing.